Short-term accumulation and elimination of carbon-14 in the common carp Cyprinus carpio under laboratory conditions

Highlights: • We investigate the short term transfer of ¹⁴C in Cyprinus carpio under laboratory conditions. • ¹⁴C (as ¹⁴C -labelled arginine or glucose) is transferred into whole body and muscle via direct and trophic routes. • Carps incorporated ~14% of absorbed ¹⁴C and ~20% of assimilated ¹⁴C. • Muscle activity represented ~30% of whole body activity, with no difference in mass-specific activity. This study examined the short term transfer of carbon-14 (¹⁴C) in the common carp Cyprinus carpio under laboratory conditions. Various experiments were achieved in order to investigate direct or trophic transfer for 4 days, using waterborne ¹⁴C-labelled arginine or ¹⁴C-labelled food pellets respectively. Radiolabelled food was prepared with ¹⁴C-labelled arginine or glucose in order to test how transfer kinetics might vary with the biochemical form of ¹⁴C. Elimination experiments were achieved using fish fed for 5 days on radiolabelled food and then placed under starvation for 4 days. In all experiments, water, food and fish activities were monitored every day. Different fish fractions (whole body, muscle) were sampled in order to elucidate the role of muscle as a potential storage. Results suggested that direct water-to-fish absorption rate was 20% d⁻¹ per fish. Carps incorporated 14.3% of the absorbed ¹⁴C. Fish activity did not increase over days, due to a strong decrease in ¹⁴C concentration in the water (resulting from aquarium sorption). During trophic transfer experiments, food was entirely ingested and ¹⁴C sources rapidly assimilated. For either arginine or glucose, results suggested that 19–20% of ingested ¹⁴C was incorporated, yielding a significant increase in fish activity over days. No difference in mass-specific activity was observed among muscle and whole body. Total activity in the muscle represented 29%–32% of whole body activity, this proportion reflecting the contribution of muscle to whole body weight. During elimination experiments, results showed a significant decrease in whole body total activity and mass-specific activity with arginine. The decrease was not significant with glucose due to a great variability among fish. Results suggested that an essential amino-acid like arginine can be used as an energy source under starvation and that muscles can act as a storage for essential amino-acids.